Transoceanic radio telephone system



June 3, 1930. H. s. HAMILTON TRANsocEANlc RADIO TELEPHONE SYSTEM 2 sheets-smeet 1 Filed .July 1e s, 1927 mVENjroR.

BY, w

` ATTORNE;l

June 3, 1930. H. vs. .HAMILTON TRANSOCEANIC RADIO TELEPHOE- SYSTEM 2 sheets-sheet 2 Filed July 16, 1927 IN V EN TOR.

TT ORNEY im SWR.,

the two-Way transmission yline withy the radio Patented June 3, 1930Y l l*SifijiTiE7S PATENT-OFFICE HAROLD s. HAMILTON, or PHOENIX, anif'zoNa, iiss'iGNon To veiyfiiizni'CAN' TELEPHONE AND minoritaria: coMrANY, a CORPORATION or, NEW troni?.

' TRANSOCEANIC RADIO l',LELEPHONE SYSTEM y Application led July 16,

4 This invention relates-to radio circuits, and more particularly tori arrangements for effecting two-way telephone communication lby means of radio apparatus. i

In connecting a two-Way telephone line to a radio circuit, it is customary to provide a radio transmitter and a radio receiver at points separated by la considerable distance, and to associate the Wire line With these two stations by a four-Wire connection. ln a system involving a long radio link, such, for `example,-as a transoceanic system, the amountA of power generated bythe transmitter on one side ofthe ocean is so large, as compared with the amount of energy receivedrby the receiver on the same side, that the transmitter and receiver must be separated by considerable distances. Even so, however, lWhereV a common' Wave length is used for transmission in both directions, it is obv-ions 'that when transmission is being sent out from the transmitting station on one side of the ocean, some positive means must -be provided Afor preventing the receiving station on the same side of the Ocean from picking up the transmitted signal.

Heretofore it has been proposed to accomplish this result byusing echo suppressorsrat some point in the four-Wire line connecting transmitter and receiver. ln order to prevent local singing over the four-Wire circuit and from the radio transmitter tothe local radio receiver, the transmitting branch of the four- Wire system is normally disabled. An echo suppressor unit is associated With that branch and is so arranged ythat When operated by voice currents, it will render the transmitting branch operative yand Will disable the receiving branch of the four-Wire circuit. A

similar echo suppressorunit associated with the receiving branch is arranged to operate in response to voice currents received by'radio from a distant transmitting station to disablethe transmitting branch-.

v Owing to the. fact that each echo suppressor `1927'. serial No. 206,342,

unit is arranged to disable the other when i tofore appliedto 'such' a branch at the point y Where the echo,suppressorunits are located. i

Experience With` ytiansoceanic radio telephony hasshovvmhotveventhat a disabling arran', ,ement controlled by f an echo n suppressor associated With 1 the transmitting ,branch and arranged toiperform its function ata point distant from the radio transmitter is unworkable Wherel al considerable amount of energyis picked up ,byv the radio receiver from the vradio transmitter during idle per rriodsof the latter. This is for thereason that during idle periods of thetransmitter,

` the transmitter is not actually quiet, but, on f the contrary, it transmits interfering Waves due to the carrier leak in the modulating apparatus to noise picked up bythe Wire line;

between the point atVWhich-the echo suppressor is located Yand the radio transmitter, and vto noisesv in the transmitter itself. All

of thesenoises are vamplified by the highpoWer ampliiier used at the transmitter, and, in some instances, the yeffect upon. the radio receiver is so great as to operate and lock up the echo suppressor associated With 'the receiving branch of the four-Wire circuit even during the so-called'idle periods of the radio transmitter. l u

p Therefore,it isproposed, according to the present invention,to apply a disabling means to the transmitting branch' of the four-Wire circuit at the radio transmitter, itself. This means is preferably applied at a point beyond themodulating apparatus,-but ahead of the ce e power amplifier, and is arranged to be operated at a distance by means of the echo suppressor associated with the transmitting branch of the four-wire circuit. The disabling means, if applied beyond the modulating apparatus, will absolutely prevent the radiation of either line noises, carrier current, or noise generated within the circuits of the radioy apparatus, itself. It is also located ahead of the power amplifier for the reason that the power amplifier does not generate any interferencewithin itself, but has the effect of greatly amplifying the energy received by it, so that a switch applied beyond the amplifier would have to commutate a very much larger volume of energy than would a switch located ahead of the amplifier.

The invention may now be more fully understood from the following description when read in connection with the accompanying drawing, Figure l of which is af diagram showing the invention as applied to a typical circuit arrangement used for transoceanic radio telephony; while Figs. 2, 3 and 4 thereof represent modified arrangements for operating the transmitter disabling means from a distance. Fig. 5 represents a modified circuit arrangement.

.Referring to Fig. 1, a typical circuit arrangement is here shown for connecting the radio transmitter and receiver at one side of the ocean with a two-way telephone transmission line. L designates such a two-way transmission line entering the city of New York, for example. This line is to be connected to aradio transmitter shown on the right-hand side of the diagram located at Rocky Point, Long Island, for example. The corresponding radio receiver might be located, for' example, at Riverhead, Long island, a town some distance from Rocky Point, and also some distance from New York. This radio receiver would also be connected to the line L. Y

In order to effect these connections, a hybrid coil 10 is provided, and the line is balanced by a suitable network N. From one vside of the hybrid coil, a connection extends through. amplifier RE, and over a two-wire line LE to a repeater station between New York and the points atv which the radio transmitter and receiver are located. In the present instance, the repeater position is assumed to be at Patchogue, Long Island. At this point, the line LE is connected through amplifiers REl and RE1 to a two-wire line LEl extending from Patchogue to Rocky Point, where the radio transmitting station is located. The radio apparatus at Rocky Point may consist of a band filter FE2 for passing a voice frequency band, an intermediate stage modulator M2 of the well-known balanced type arranged to suppress the carrier, the band filter FE2 for suppressing one of the side bands resulting from the first stage of modulation, for example, the lower side band, and a second modulator M2 of the carrier suppression type, by means of which the selected side band may be modulated upon a higher carrier. A band filter FE2 is located on the output sidev of the modulator M2 for selecting one of the side bands which is finally to be transmitted from the antenna AT. The power amplier FA is a high power arrangement of well-known type, which amplifies the side band currents selected by the filter FE2 and applies them to the radiating antenna.

YWhile both modulators M2 and M2 are arranged to suppress the carrier, complete suppression is not actually possible by virtue of a balanced arrangement, and consequently, some carrier energy will be radiated from the antenna AT during idle periods of the transmitter. Furthermore, even if no carrier leak occurred, noises picked up by means of the line LE1 from other lines in the same cable, as well as noises generated in the modulating apparatus itself, would produce side band modulations of the carrier which would be radiated by the transmitting antenna AT. In a typical case act-ually'encountered in connection with a radio telephone system between New York city and London, it was found that the radio transmitter located at Rugby, England, radiated, during idle periods, an amount of energy such as to produce upon the receiving station located at Wroughton, England, a distance of about 8O miles from Rugby, an eect comparable with that of the desired signal from New York. lt is therefore obviously necessary to provide some means for actually disabling the radiotransmitter, itself, during its idle periods.

Before describing the disabling means, however, `it should be noted that the radio receiver, which', in the case illustrated, is assumed to be located at Riverhead, Long island, and which is schematically indicated at RR, is connected to the Patchogue repeater station by means of a line LW3. Atthe repeater station, an amplifier RlVl is interposed between the line LW3 and a line LN running from Fatchogue to New York, at 'which point a one-way amplifier Rl is interposed between the terminals of the line LW and the hybrid coil 10, through which it is associated with the telephone line L.

Coming, now, to the echo suppressor apparatus, an echo suppressor equipment, comprising an amplifier-detector DW1 and a voice-operated relay VRl, is bridged across the line from the radio receiver to Patchogue on the output side of the amplifier Riil. This apparatus is of the type well known in the art, and it is therefore unnecessary to describe it further than point out that the general effect of the amplifier-detector DW,V is to amplify and rectify voice currents so that a direct current component thereof energizes'the voice-operated relay'VRlgf- A ysim;l

ilar echo suppressor unit comprises an amplirunning from New Yorkl to the radiotransmittel'. `Preferably, this bridge is applied on theoutputside of the amplifier PE1. The' echo 'suppresor unitasociated with the receiv ing line controls a contact l,"whic h,-when the distant transmitter is talking, isl operated to short circuit the line Lid-LE1 at Patchogue. Y

' Anoise originatingin the high-power amplifier This sameV contact also short circuits-the echo Suppressor unit` DEl-DR1 'associated with,

Vthe transmitting line, thereby vpreventing false operation.F Similarly, the echo suppres' sor unit associated with the transmitting vline controls a contact 2 which, when the -subscriber at the distantend of the line Lis talking, functions to Ashort c ircuitfthe receiv-'" ing, line LW-LW3Lg* This'contact also short Ycircuits the echo suppressor unit controlling the Contact l to preventfalse operation.'

In order to preventsinging over the local circuit,'comprising the four-wire system and the radio path from the local'transmitting Aantenna AT to the local receiving antenna RT, it has heretofore been proposed to provide the echo suppressor unit fDEl--DRl with talks, the contact 2 isoperated to disable ythe lline'transmitting,from east to west; and theV ,95 f

a second vconta.ctl normally short cir'ouiting the line LE1 at Patcliogue This would have the eifect of normally disabling the trans-- mission path.V YVhenfthesubscriber on the telephoneline talks, however, the echo suppressor unit DEl-VRl would open this contact so that transmission could take place between New York and the radio transmitter.

In order to providethe necessary time where-` by this contact could be opened bythe echo suppressor unit before the voice wave initiatingl the operation" should have arrived at vthe point wherethevshort` circuitfwas 'to be applied, a delay circuit X is interposed between the bridge point A and the short Vcircuitlng point, whichin systems heretofore proposed has been located at B. [If Vdesired,an'addi tional one-way amplifier RE.1 may be prol vided to make up for thetransinission loss introduced by the delay circuit. l Y

lAn arrangement such as above described would be effective were it not for the interference radiated fromlthe antenna AT during idle periods of, the transmitter., Ashas already beenpointedout, this interference is due to incompletesuppression of the: carrierandalso to modulation of ythe carrier by a line noise picked up by the,` line LEI, and also 4noise generated inthe modulatingl apparatus, l itself. In order to'overcome'this diiiiculty,vit f is proposed, in accordancewith the present invention, to replaceorsupplement the short circuit at lB by a short ,circuiting contact 4f at the point C justbeyond thesecond moduj fJlator M2 of the, radio. transmitter, Jandjust ahead ofthe high-power amplifiers PA. i A short'circuit applied at thisV point will have.,

either in the .modulating apparatus orin the transmission line running from New vYork to the. radio transmitter. By arranging the.

`shortcircuit, on-thelinputsi'de of:` the powerl amplifier, theamountofL energy which it 'is required-tocommut'ateis quiterminute as compared with the, energy which it would bere- :quired to control if located onthefoutputf side of' thel amplifi'erfPA. -Tbeainount of PA is practically negligible, so that it'is'quite -possible to locate the short c irc'u'itingk con tact 4 at the point indicated and stillattain the desired effect.

1 In order to control the contact from the P'at'chogue repeaterYA station, thevbr'i'dgel terminals" at A may be connected at, the latter station to an 'auxiliary line AL' running from .Patchogue toRock'yfPoint, and,at the latter y station, an ampliiierdetector yDE2 and a voice relay VR2, similar tothe corresponding 'ele'- ments already described'A at Pat'chogua are located at `Rocky Point, at the terminaluof the line AL., The voice-operated relay' VR2 controls fthe contact sothat whenever the subscriber'at'the distant end-of/theline L Vshort Vcircuit 4 is removedY at the point"C,thus

tio-east., l ',Brief-ly,'thefop'eration is asefollow's: Normally/the contact 4 completes a, short cir-i cuit at the 'point @,so 'thatno noise originating ln'rthektransmitting line or inthe radio apparatus Ican be radiated byv the antenna AT. Hence, 'no 'noise ispicked up bythe re'ceiving antenna RT during yidleperiods off V'the transmitter.l If transmission 'is being received fromthe distant transmitting apparatus,i,it y will Vbepcked u`p by the'antenna 'RT Iand translatedto audio'form by radio receiver RR at Rocky, Point.l r"The Vaudio telephone currents-fwill bethen transmitted over the line LW3 toPatchogueand ,amplithe amplifier, BWL, The amplified currents-arethen transmitted over theiline.

suppressor unit DEg--VRZ at Rocky Point. Thus, during receptionythe 4entire transmitting channel between'New York andfRocky Point is inoperative. the shortcircuiting contact l were not provided, an echo current "passing throughv the line;- LW ,and through the hybrid coil lOmight pass'over the line LE andoperate the echo suppressor unit f To l Lw and through `um amplinerfnwfto s165115 Vline LQ Partfof the energy'amplifiedbythe amplier RWl atPatchogue, however, f serves to operate the voice relay VRI and closescontact e 1}therehyv short circniting the lineLE-l-LEl; v120 at A,'and also disablingthe echo ,suppressor f unit DEl-VRh'aas well as the dist'ant echo associated with vthe transmitting channel and thereby cause a false operation.

Vhen transmission is not being received from the distant point, and the subscriber associatedwiththelineLtalks,thevoice currents are passed from the line L through the hybrid coil 10, through the amplifier RE and over the line LE toPatchogue. Here, the amplifier RE1 amplifies the voice currents and impresses them upon the delay circuit X. While passing through the delay circuit (which may obviously be located at any point between A and C), a part of the ampli- `lied energy is diverted into an echo suppressor DE1-VR1, thereby operating the contact 2 to short circuit the line LWB-LW.

- Also, the echo suppressor unit DE2-VR2 side band. The upper side band is then impressed uponthe second modulator ME2 to modulate the carrier supplied thereto. This Acarrier-likewise is suppressed, and-both resultant side bands are applied to the filter FEf2 -which again suppresses one of the side bandsand permits the remaining side band .to pass to the power amplifier PA (the contact 4 having been opened by this time). The lpower amplifier PA ampliies the side band currentsfor transmission to the distant receiving station. l

The arrangement illustrated in-Fig. 1 has the disadvantage of requiring two echo suppressors associated with the transmitting channel,-one.at Patchogue and one at Rocky Point. Fig. 2 illustrates an arrangement by which one echo suppressor unit will perform both functions. Here, the detector tuberi)1 of the amplifier-detector unit DE1 has its plate circuit connected through a relay VRl,

located at Patchogue, to a line wire A eX- tending to Rocky Point. Here, the line wire ris connected to one terminal ofa similar rerlay VRZ, the other terminal of the relay being connected over a return wire 41 to a B battery located at 'Patchogue The relay VR1 will control the contact 2, as in Fig. 1, and similarly, the relay VR2 will control the contact 4, as in Fig. 1. The line wires 40 and 41 may be simplex circuits derived from telephone pairs in ordinary ytelephone cables. 'It will, of course, be obvious thatthis arrangement ismuch cheaper than the arrangement illustrated in -Fg- 1.-

An alternative arrangement employing only a single line wire between ,Patchogue and Rocky Point, for operating thev relays l VR1 and VR2,;is shown in Fig. 3, where the B battery is connected directly to the terminal of the relay VR2 and there grounded. This arrangement has the disadvantage, as compared with the arrangement of Fig. 2, that it is more susceptible to interference impulses picked up from the ground. Another modiiicationis illustrated in Fig. 4, in which the relay V1R2 is controlled through a Contact o f the relay VRl instead of being included directly in. the plate circuit of the detector tube as in Figs. 2 and 3. Normally the relay VR2 is deenergized by reason of the fact that the upper Contact of the relay VR1 short-circuits its winding, a resistance 45 beingincluded inseries with the oper-- ating battery of the relay VRZ to prevent the short circuit from running down the battery. Whenever voice currents operate the detector tube so that the relay VRl is energized, it causes the operation of the distant relay VR2 by opening the short-circuit above described. A further modification is illustrated in Fig. 5, this modification being along the lines of F ig. l in that a separate echo suppressor unitis provided at the repeater station and at the distant radio transmittting station, but in this case, the echo suppressor unit at the transmitting station is connected to the transmission line locally so as to be operated by voice currents transmitted over the normal telephone transmission line instead of over a supplemental line. In order to accomplish this resulta` delay circuit X2 is inserted at the Rocky Point transmitting station ahead of the band filterFEg, shown in Fig. 5, and the amplilier-detector DEZ is bridged across the line terminals ahead of the delay circuit X2. The auxiliary line AL, provided in Fig. 1, is omitted entirely7 and voice currents to operate the amplifier-detector unitDEZ are transmitted over the regular transmission line LEl. The delay circuit X2 is necessary to enable the relay VR2 to remove the shortcircuit at 4 before .the voice currents (which cause the operation of the relay VR2) have had time to reach the point at which the short-circuit is applied. The amplifierdetector unit DEl, at the Patchogue repeater station, will be arranged as inl Fig. 1 to apply a short-circuit at 2 to the receiving path LW3. TWhile not essential to the arrangement of Fig. 5, the relay VRl may also be arranged to apply a short-circuit 3 to the transmitting line at the point B,.in which case the delay circuit X will be provided, as shown, to enable the relay VRl to remove the short-circuit before the arrival of the operating voice currents. This arrangement is desirable because it is essential that the receiving path always be disabled whenever the short-circuit p 4 is removed fromjthe transmitting'palth at C.

lIl() unit DEZ,y which in-'turnfremoves the vshort-pV Y ting path operablel apparatus) s it is necessary tocontrol this Jdisablement of the receiving path rom-.theamplifier-detector unit DE1, .it might happen that if the ampliier-detector unit DEZ were more sen-v unit DEifwould respond lto weak noise curi rents andremove the shortcircuitat C, while the unit DEl would not .disable the receiving j path. Therefore the unit DE1 isarranged: to

control a local shortcir'cuit 3 atB, sothat.

noise currents transmitted fromk the line L over the transmitting path 4will' not arrive at C to vcause false operation in themanner above described. On vthe other hand, voiceA currents transmittedfrom theline L will operate the ampliendetector unit DEl to short-K'` circuit the receiving ath at Zandt-o remove the short-circuit 3 at cause the operation of the amplifier-detector circnit 4 at C, lthusfrenderin'g the transmit- This modification hagais-obvious advantage thatV the auxiliary line AL of Fig. 1 may beY dispensed with. The arrangement also has the advantage over FigsQ, 3 and 4, that where the auxiliary line,l whether it be a one'-v wire or two-wire circuit,.is of considerable length (because of the distance between the repeater station and the radio transmitting v` *tional amplifier-detector unit at: the radio Y It will beobviou'sthat thegeneral princi?v line to the V transmitter, .'a 'secondi'V ofne-ways` path' for transmittingcsignals"5 'from i saidn transmitter station than to provide anauXili iary line between the repeater station and the radio'transmitter station.

ples herein disclosed 'fmay be embodied: manyAot-her organizations widely, .different from those illustratedwithout "departing theffollowing claims. -v

from the spirit of the inventionl as fdened inu3.:Injasignalingsystem, a-vtwo-way-tele-ff phone transmission line, af radio transmitterincluding a modulatorrfal radio.re`ceiver, af

" 7. Inja signaling *system*7 r`a='twoway tele-ly transmitting antenna into which said moduphone transmission line, a radio transmitter including amodulator,v a radio'- receiver;a` transmitting antennafinto which saidmoduf;y latorzgworks;y 'a receiving antenna separate".

fromsaid-transmitting antenna and V asso ciated with saidrradloreceiver, a first one?r way path between said line* and said' 2 radio radio receiver V`Ltok'said line,fecho suppressor 1 equipment located atea pointfthroughwhich1 fboth o-said paths pass, said echo suppressor yequipment comprising* an Yecho suppressor unit associated with the'-rst .Pathgand re-l sponsive tojsignaljs;transmitted theoyr to disable they second path, a' ysecond echoff .Y presser-*unit associatedwith thesecondpath 1 and responsive to Asignals transmitted.'there ,l over for ldisabling rsaid ir'stpathfa'fdisabling" means normally applied c'n' the output'ffside whereupon the voice currents are transmittediover the lin'eLEl/ tol it is cheaper to provide an` addi-f tween: said modulator` and the transmitting antenna .to 'prevent the 'radiation of interference. during idle periods of the .transmitter,

sitive than the similar arrangement DB1-, the 5 'and means responsive -to the kapplication of signalsrtolsaidrst path-.fior removing said last mentioned disabling means f in response tovoice currents appliedt'ojsaid first mentioned one'eway path.A

.Y `2.` ln a. signaling system, a two-way teleincluding a modulator, a radio `rreceiver, a

, l. .75 phone transm1ssion l1ne5 a radiotransmitter I transmitting antennainto which said'modu-k L lator works', a receiving antenna` separate i from said transmitting antenna land'assoway path 'between said line 'and said. radio transmitter for transmitting signals from the line/to the transmitter, a second vone-wayV path for transmitting signalsfrom saidradio receiversto said line,` echo suppressor equip# ment located at a point through which both of saidl paths pass, said` echo suppressor l n equipment comprising an echo suppressor unitlassociatedwlththe first path and responsive toi signals transmitted thereover to disable the second path, a second echo'snp-l pressor unit associated with the second path and'responsive .to Vsignals'"transmitted there-j overfor disablingsaid rst path, al disabling means normally applied onV the outputv side A o'ffthe `modulator ofthe radio trans'mitterfbe-A tween said modulator `and the transmitting'r antenna to prevent the radiationofinterferencegduring. idle periods-of the transmitter, and: means responsive tothe application of ysignals to' said first path and controllable from the point at which said echosuppressor equipment vis llocatedior removing said disabling means in responsetoY voice cnrrents applied to said rst mentionedfonewaypath.

lator Y works, f a receiving antennaseparate *from-saidl'transmitting'antenna'andnassocif f ated withxsaid,-radioreceiver, a iirst one-way pathl between said line "and said radioitr'ans! VVmitter for,transmittingv signalsffromthe line Ytol the transmitter, a second'oneiway pjath for transmitting signals from saidV radiolreceiverl l atedtwith the irst path and-responsive to sig? hals*transmittedl thereover Vtodisablelthe*sem; e

i to iy said glinef. echo Y snppressorj' `equipment lo f cated.at'apoint through which' both of"`said paths p lass,` saidiecho 'suppressor equipment comprising an' echo "suppressorwunilt'fassocie I ond'Y path, afsecond' echo suppressor yfunit as# 1 sociated with'thesefcond pathandlresponsiv@ `vtosignals 'transmittedthereoverfordisabling e Y saidfiirst! path,-

'sho'r'tfcircuit normally: ,l Y `appliedongtheoiitputlside of*thej.'modulatorr for 'saidr'adi'o tra"ns'mitter-betweenl said'modu A y l'atOr and the vtransinittingantenna-to[prei vent the radiation of interferenceV during Vthe idle condition of said transmitter, and means controllable from the pointat which the echo suppressor equipment is-applied for removing said short circuit in response to the application of voice-currents from said telephone line to said first-mentioned path.

4. In a signaling system, a two-way telephone line, a radio transmitter and a radio receiver, said radio transmitter comprising means for modulating the carrier frequency in accordance with speech and a power amplifier lfor amplifying modulated oscillations in their high frequency form, a first one-way path for transmitting signals from said twoway line to said radio transmitter, a second one-way path for 'transmitting' signals from the radio receiver to said two-way line, echo suppressor equipment located at a point through which both of said one-way paths pass, said echo suppressor equipment comprising an echo suppressor unit associatedrwith said first one-way path and responsive to signals transmitted fromlsaid telephone line to the radiotransmitter to disable said second path, a second echo suppressor unit associated with the-second path responsive to signals transmitted from the radio receiver to a ylinevto disable said first path, disabling means normally applied to said radio transmitter between the youtput side of the modulator thereof and the input side of the high fre-.-

quency amplifier thereof, and means controllablefrom the point at which said echo in accordance with speech and a power amplifier for amplifying modulated oscillationsl in their high frequency form, a rst 'one-way: path for transmitting signals from said twoway line to said radio transmitter, a second4 Vone-way path. for transmitting signals from thel radio receiver to said two-way line, echo .suppressor equipment located at a point,

through which both of said one-way paths pass, saidecho suppressor equipment comprising an echo suppressor unit associated with said first one-way path andresponsive tol signals transmitted from said telephone linev to theradio transmitter to disable said second path, a secondecho suppressorunit associatedV with thesecond path responsive to signals transmitted from the radioreceiver tothe line to .disablesaid rst path, a short circuit normallyapplied to said radio transmitter 'between the output rof theV modulatorv thereof.'

a and the input-ofthe high-frequency amplifier thereof,'said short circuitfunctioning to normallyprevent the radiation of interference during idle'fperiods of the transmitter, and means controllable from the point at which said echo suppressor' equipment is located and responsive to telephone currents applied i to said first one-way path to open said short circuit.

6. In a signaling system, a two-way telephone line, a radio transmitter including a modulator, a radio receiver, a transmitting antenna into which said modulator works, a receiving antenna Yseparate from said transmitting antenna and associated with said radio receiver, a first one-way circuit for transmitting signals from said telephone line to said radio transmitter, a second one-way circuit for transmitting signals from said radio receiver to said'two-way line, echo sup. pressor equipment located at a'point through which both one-way paths pass, said echo suppressor equipment comprising an amplifying and rectifying unit associated with said firstmentioned path, a relay associated with said unit andresponsive to voice currents Ytransmitted over said first one-way path to disable said second one-way path, a second amplifying and rectifying unit associated with said second path, a relay associated with said second unit and responsive to rectified voice currents transmitted over said second path to disable said first path, a normallyfdisabling means applied on the output side of the modulator of said radio transmitter between said modulator and the transmitting ant-enna for preventing the radiation of interference during Vidle periods thereof, and a relay for controlling said disabling means, said relay beingconnected to be operated by rectied voice currents from the output of said first-mentionedamplifying and rectifying unit.

7. In a signaling system, a two-way telephone line, a radio transmitter including a modulator, a radio receiver, a transmitting antenna into which said modulator works, a receiving antenna separate from said transmitting antenna-and associated-with said radio 'receiver, a first one-way circuit for transmittingsignals from said telephone line to said radio transmittenfa second one-way circuit for transmitting signals from saidradiol receiver to said two-way line, echo suppressor equipment locatedat a point `through which both one-way paths pass,said echo suppressorequipment comprising an amplifying and rectifying unit associated with said first path, a relay connectedfto Vthe output side of said unitgand-responsive to rectified voice currents transmitted over said-firstV path to apply a short .circuit to said second path, an amplifying and detecting unit associated with said second-path, arelay-connected to the output side of .said second unit andl responsive to rectified voice currents transmitted over said second'pathgto short circuitsaidgrst path, a short; circuit normally applied von the output sideof modulator of said radiotransmitter between said modulator and the transmit-q Y* ting antenna for preventingthe radiation of f interference during idle periods ofthe transname to this mittel, and a relay for removing said lastmentioned short circuit, said relay being oonnected to be operatedby reetied'voice currents Afrom the output of said rst-mentione amplifying anddetecting unit.

1n testimony whereof, I have signed my specification July l1, 1927.

HAROLD S. HAMILTON.y 

